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f   ,                         978                                Appendix F.

I  ;                     .                                       CHAPTER VI.

I  |                             ./^. 200 and 814.   The Turret-head Lathe.A very

1 I  /                        excellent and powerful form of this useful tool is manufactured

by Messrs. Alfred Herbert, Limited, that known as the ' No. 6
tiexagon Lathe' being illustrated in Plate XIX., Figs. 904-5-6,
and in Fig. 907. Being strongly built it is suitable for any
heavy chuck work that can be made in quantity, such as cylinder
covers. Described generally, it is driven from a two-speed
counter-shaft, has two sets of back gears, and two sets of change-
wheel driving gear for the saddles. The saddles are two, one
carrying the secondary or intermediate head with four tools for
external screwing or bar work, and the other supporting the
principal or hexagon head for internal work generally. The
latter can carry six special bracketed tools of large size.

The Fast Headstock, shewn in Plate XIX. and in Fig. 907,
carries in parallel bearings the hollow mandrel B, through which
material of 2^" diameter can be fed. The cone pulley c, riding
freely, has three steps of 13", 15$', and 18" diameter respectively,
taking a belt of 4' wide, and has spur pinions E and H fixed to
its left end, which gear with wheels G and H on the back shaft.
The spur wheel K also rides freely on the mandrel, and gears
with pinion j on back shaft. D arid L are friction clutches fitting
loosely in the cone pulley c and spur wheel K respectively, and
keyed to the mandrel, while M is a clutch arm capable of sliding
| I                        on a feather key. The arm M heing moved lengthwise by the

*"                           pinion N from the lever Q, acts upon toggles at R, and expands

the clutch rings in D or L, so that the cone c or the spur wheel K
may be fixed to the mandrel at will. In a similar manner the
lever tr may be moved to right or left, thus turning shaft T and
sector R, and traversing sleeve s upon shaft v. A loose collar w
and a pin connect sleeve s with the inner spindle x, and thus the
sliding motion of s is transferred to the small roller which lies
between the sliding wedges z z, causing one or the other of these
wedges to be moved outward, expanding the clutch ring a in H
or G. In this manner the spur wheels H or G are individually
1 *                        fixed to the shaft v, providing an immediate change from a back

gear of 4-3 : i to one of 15-8 : i.   As there are two speeds on the